The Event Loop, Microtasks, and Asynchronous Concurrency
Asynchronous execution is the single most tested topic in modern FAANG frontend interviews. Interviewers frequently present interleaved code combining `setTimeout`, `Promise.resolve`, `queueMicrotask`, and async functions to evaluate whether you truly grasp the browser runtime event loop.
Our interactive lessons step through the exact microtask queue draining cycle that happens before the next macrotask or browser rendering tick. Learn how to write resilient Promise chains, handle edge cases with Promise combinators, and build production-grade concurrency throttles.
Interview Modules (7)
1. Event Loop & Microtasks
Interactive ReadyWhat is the exact order of numbers printed to the console when the following JavaScript snippet executes?...
2. Promises & Chaining
Interactive ReadyWhat output is logged to the console when the following promise chain executes, and how do errors propagate th...
3. async/await Internals
Interactive ReadyWhat is the exact sequence of outputs printed to the console when the following JavaScript code executes, and ...
4. Promise Combinators
Interactive ReadyWhat is logged to the console when the four Promise combinators execute with a rejected and a resolved promise...
5. Timers & Concurrency Control
Interactive ReadyWhat is logged to the console when the following timer and microtask scheduling code executes, and how does th...
6. Promise Concurrency Pool
Interactive ReadyWhat is logged to the console when the following promisePool utility executes four tasks with variable delays ...
7. Async Iterators & Streaming Backpressure
Interactive ReadyWhat is logged to the console when the following async generator pipeline is consumed with for await...of and ...